System of motor control



1,614,198 11 1927' B. w. JONES SYSTEM OF MOTOR CONTROL Inventor: Beru'amin W Jones;

Hi 5 Anborneg- Patented Jan, 11, 19 27.

UNITED STATES 1 1,614,198 PATENT OFFICE.

BENJAMIN W. JONES, 0F SCHE NECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

SYSTEM OF MOTOR CONTROL.

' Application filed July'21,

For certa'n applications such as the driving of rolling mills, mine hoists, and the like in which the load is apt to vary materially, it has been common practice to store energy in some movable part during l'ght loads so that when the load, on the driving motor exceeds a predetermined vaiue, the stored up energy may be used to relieve the motor. Fly wheels have heen used to store up and give out energy for this purpose and alternating current motors of the type in which the speed may be varied'by varying the resistance of the rotor c rcuit have been commonly used for driving the variable load. Arrangements have heretofore been provided for re-inserting the resistance in the rotor circuit of the motor in response to the load on the motor in order that the fly wheel may give up its stored energy and thus assist the motor to carry the heavy loads. Such arrangements as heretofore provided have left somethng to 'be desired in the simplicity, reliability and general effectiveness of the means provided for insuring that the resistance in the rotor circuit shall not be immediately again short circuited after the reinsertion thereof in the rotor circuit. When the resistance in therotor circuit, or a sec tion of the resistance, is re-inserted in the rotor circuit n response to the occurrence of a heavy load on the motor so that the slip of the motor is increased and the fly wheel may give up )art of its stored energy, the current taken y the motor will be decreased temporarily-and after an interval the current will increase. Unless special provis'on is made therefor, the resistance in the rotor circuit will be again short circuit-ed during th's interval and thus defeat the object of permitting, thefly wheel to carry a part of the load during the time in which the load on the motor is above the predetermined value.

The present invention has for its principal object the provis'on of an improved con trol for an electric motor wherein simple, reliable and effective means is provided for taking care of the conditions referred to above.

For an understanding of the invention reference should be had to the accom anyng drawing wherein I have shown w at I now regard as the referred form of the invention in avery snnplified system of motor control.

1924. Serial No. 727,113.

Referring to the drawing, the electric motor .10, which is indicated as of the 3 phase alternating current type having slp rings 11, 12 and 13, is arranged to be connected to the source of supply 14' by means of the line contactor 15. The motor is arranged to be accelerated and generally controlled by means of the resistors 16, 17 and 18 included in the rotor circuit of the motor. The contactor 19 is provided for short circuit'ng the resistor 16, the contactor 20 is provided for short circuiting the resistor 17, and the contactor 21 is provided for short circu'ting the resistor 18. These mesistor contactors are arranged to be under the control of the master switch 22, and the electro-responsive relay 23 is provided for controlling the energization o ;the contactor 19. the relay 24 is provided for controll'ng the resistor contactor 20 and the relay25 is provided for controlling the resistor contactor 21 so as to effect the reinsertion of the respective resistors 16, 17 and 18 in the rotor circuit of the motor in response to the current taken by the motor. The current lim't relays 26 and 27 are provided for controlling the resistor contactors 19, 20 and 21 in response to the current taken by the motor at starting so as to eflect the successive energization of the resistor contactor and thus the successive short circuiting of res'stors 16, 17 and 18 during the acceleration of the motor. As will be hereinafter explained, the current limit-relays 26 and 27 are arranged to operate alternately in the control of the resistor contactors. The current responsive relay 28 is provided for controlling the relay 23, the

current responsive relay 29 is provided for controlling the relay 24 and the current rcsponsive relay 30 is provided for controllingthe relay 25 so as to automatically control the energization of the resistor contactors 19, 20 and 21 respectively for the purpose of automatically reinserting the resistors 16, 17 and 18 respectively in the rotor circuit of the motor after the motor has been accelerated and brought up to speed and the load on the motor exceeds a predetermined value. T he motor 10 is provided with a flywheel or other inertia load which is indicated at 31, the idea being that energy will be stored in this inertiaload so that when an excessive load is encountered by the motor 10, the resistors 16, 17 and 18 may be introduced in the rotor circuit of the motor so as to permit the inertia device 31 to give up a part of this stored energy and thus assist the motor CFI till

in carrying the temporary overload.

As thus constructed and arranged and with the parts in their respective positions shown in the drawing the operation of the arrangement is as follows: In case the master switch 22 is thrown from the off positicn, that indicated on the drawing, to the full running position, the line contactor will be energized to close and thus connect the motor to the supply circuit 14. The resistor contactor 19 will be energized to-close through the auxiliary switch associated with the line contactor 15, contacts 32 of therelay 23, the auxiliary switch 33 associated with the contactor 19 and the ooil34 of the relay 26 to the upper supply conductor.

However, the contactor 19 will not necessarily close at this time to short circuit the resistor 16, because of the fact that the coil 34 ot' the relay 26 is included in series with the coil of the contactor' 19. The energization of the coil 34 of the relay 26 will cause the plunger associated with this coil to-be attracted and thus move the lever 35 out of engagement with the lunger '36 so that this plunger will be held in the position shown in the drawing by the winding 37 as long as the current taken by the motor in starting is above a predetermined value. \Vhen the current taken by the motor has dropped to the predetermined value the energization of the coil 37 will be insufiicient to hold the plunger 36 in the upper position and this plunger will drop thus closing the circuit through the contacts 38 and tempo rarily short circuiting the coil 34 of the relay. This will put substantially full line voltage on the coil of resistor contactor 11) so that this contactor will be energized to close and short circuit the resistors 16. The short circuiting of the coil 34.- of the relay 26 will permit the plunger associated with this coil to drop to the position shown in the drawing and thus raise the plunger 36 Zll'lti '1 the circuit through the contacts 33 preparatory to subsequent operation of the relay. llhen the contactor 19 closes, a maintaining circuit for coil of the contactor is established through the auxiliary switch 39 so that this contactor will be maintained closed independently of the operation of the rela 26.

The coil of the resistor contactor will be energized through a I cuit from the middle supply conductor, the third contact linger of the master switch 22, the contacts 40 of the relay 2%, the auxiliary switch 41 associated with contactor 20, the auxiliary switch 4-2 associated with contactor 19, coil 43 of relay 27 to the upper supply conductor. Because of the fact that the coil 43 of relay 2'2 is included in series with the coil of contactor 20 this contactorwill not close until the current taken by the motor has dropped to the predetermined value and the circuit through the contacts .44 of relay 27 are closed under the control of the current coil 45. in a manner similar to that previously explained in connection with the operation of the relay 26. When the circuit through the contacts 44 is closed the contactor 20 will be energized to close and this contactor will be maintained energized through the auxiliary contact 46 independently of the subsequent operation of relay 27. When the resistor contactor 20 closes. the coil of resistor contactor 21 is energized through a circuit from the middle supply conductor and the second finger of the master controller 22, the contacts 47 of relay 25, auxiliary switch 48 associated with contactor 20, coil 34 of relay 26 to the upper supply conductor. The resistor contactor 2 will be energized to close under the control of the current limit relay 26 in a manner similar to that previously explained in connection with the resistor contactor 19, and this resistor contactor 21 will be maintained energized through the auxiliary switch 49 associated with contactor 21.

Assume that the motor has been thus accelerated and that all of the resistance in the rotor circuit has been short circuited and that the motor is running at approximately normal running speed. In case the current taken by the motor exceeds a predetermined value during the normal operation of the motor, the current responsive relay 30 will be sufiiciently energized so as to control the relay to effect the deenergization of the rotor resistor contactor 21 and thus effect the reinsertion of the resistors 18 in the rotor circuit of the motor.

It will be observed that the relays 23, 21 and 25 are identical in construction and in their general connections. A detailed explanation of relay 25 will be now given in order that a complete understanding of the operation of these relays may be had. it will be observed that the contacts i? of this relay are arranged to be in the closed position by reason of the energization oi coil 50, and that the coils 50 and 51 of the relay are arranged so as to be normally in series across the upper and the middle supply conductors so that the contacts 47 will he maintained closed magnetically by the coil 50. When the switch member 52 of relay is operated so as to malte engagement with the contact 53 in response to the overload on the motor, the coil of relay 25 will be short. circuited through the switch member 52 and contact 53 of relay 30, so that the full potential across the upper and middle conductors of the supply circuit will be applied to the coil 51 of relay 25. This will cause the plunger associated with coil 51 to rise and thus open the contacts 47 through the iao lever 54. A timing device is provided for insuring that when the resistor contactor 21 has been thus opened and the resistors 18 are reinserted in the motor circuit, that the contacts 47 will not be reclosed during the interval in which the motor'current temporarily drops due to the'reinsertion of the resistors.

This time device is preferably of the type disclosed in the application of George E.

Stack, Serial No. 636,456, filed May 3, 1923,

and is indicated in very diagrammatic form on the drawing. As shown, the timing device comprises a switch member 55 which is resiliently connected to-the plunger associated with the coil 51 so that when the coil 51 is energized to pull up the plunger, the switch member 55 will be put under'a strain to the closed position. This switch member will be magnetically held by the electromagnet comprising the winding 56 and the armature 57 which is secured to the switch member 55. This armature 57 is arranged to be alternately held and released in response to the flux emanating -from the coil 56. B reason of the fact that the switch member is put under a strain to the closed position and by reason of the fact that the coil 56 is energized from analternating current circuit, the armature 57 will be alternatelyheld and released and when the armature is released, the switch member will bepermitted to advance step by step to the closed position. This will take an appreciable time and this time interval will be sufiicient so that when the switch member 52 of relay 30 returns to the position indicated on the drawing due to the fact that when the resistors 18 are reinserted in the motor circuit the motor current will temporarily drop, the coil 51 of relay 25 will not be short circuited for an interval of time, which may be predetermined. W'hen the resistors 18 are included in the motor circuit the flywheel 31 will be permitted to give up a part of its stored energy and thus assist the motor in carrying the overload.

When the current taken by the motor increases after the temporary reduction. in

the motor current occasioned by the reinsertion of the resistors 18, and the switch mem er 52 of relay 30 returns into engage ment with the contact 53, in case the time interval device associated with relay 25 has functioned so that the switch member 55 has been operated into engagement with its hand contact, thereby short circuiting the coil 51 of relay 25 through a circuit which includes the switch member 55 of relay 25. When this happens, full potential will be applied to the relay coil 50 and the switch member 47 will be magnetically operated to T the closed position so as to energize the rotor:resistance contact-or 21 to again short circuit the resistors 18.

In order to provide for inserting more or less of the resistance in the rotor circuit T depending upon the value of the overload to which the motor is subjected, the relays 24 and 23 are also provided. Relay 24 will be operated to control resistor contactor under the control of the current responsive $0 relay 29 in a manner similar to that explained in connect-ionwith relay 25 and reay in the control of resistor contactor 21. The resistor contactor 19 will be similarly controlled by the relay 23 under the control of the current responsive relay 28 in a similar manner. Current responsive relays 30, 29 and 28 are preferably adjusted so that for an overload of a certain value the relay 30 will operate, fora-n overload of the motor to make the motor carry part of the load.

It will be observed from the foregoing that the arrangement provides a very simple and effective means for insuring that the resistance in the rotor circuit will not 105 be again short circuited during the interval in which the current taken by the motor decreases immediately after the reinsertion of the resistance in the rotor circuit. The

timing (lBViCiS associated with relays 25, 24

and 23 may be adjusted so that the motor current wiil have an opportunity to again increase before these relays will be operative to again short circuit the resistors in the motor circuit. In other words, the resistance will not be again short cireuited after-the reinsertion thereof in the motor circuit until after the flywheel or other inertia load has been perm tted to give up apart of its stored energy and thus assist the motor in carrying the driven load. However, it. will be observed that as soon asthe motor current" has dro ped to-the predetermined value or values etermiued by the settingof' the relays 30, 29 and 28 after this time interval has elapsed, the relays 30, 29 and '28 will be operated to efi'ect the short circuiting of the resistance in the rotor circuit under the control of the relays 26 and 27.

The invention is. not necessarily limited arrangeto a system employing a flywheel or other inertia device in connection with the motor, since the invention is applicable to other uses, as for example, loads such as dredges where the loading means becomes fouled and the driving motor may stall while the load ing means is be ng loosened. While I have shown and described my invention as applied to an alternating current motor, the invention is not necessarily so limited but is applicable to other types of motors, as will be understood by those skilled in the art from an understanding of the invention.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown is only illustrative, and that the invention can be carried out'by other means.

What I claim as new and desire to secure by Letters Patent of the United States is l. The combination in a system of motor control, of a motor, a resistor in the motor circuit, a switch member operable between an open position and a closed position for efiecting the short-circuiting of said resistor and the reinsertion thereof in the motor circuit, and electroresponsive means responsive to the motorcurrent for effecting operation of said switclrmember to one of said positions to efiect the reinsertion of said resistor in the motor circuit, the said means including an electroresponsive time element device, set in operation when said switch member is operated to effect the reinsertion of said resistor, for.holding said switch member insaid operated position for a definite interval of time to thereby revent the short-circuiting of said resistor uring said interval.

2. The combination in a system of motor control, of a motor, a resistor in the motor circuit, a switch member operable between a closed position in which the short-circuiting of said resistor is effected and an open position in which the reinsertion of said resistor in the motor circuit is effected, and electroresponsive means responsive to the motor current for effecting operation of said switch member from the closed to the open position, the said means including an electromagnetic time element device, set in operation when said switch member is operated to the open position, which prevents said switch member from moving: from the open position for a definite interval of time to thereby prevent the short-oircuitin; of sa 'l resistor during said interval, the said device being arranged to restore exclusive control of said switch member to said current responsive means after the expiration of said time interval.

rename 3. The combination in a system of motor control of a motor, a resistor in the motor circuit. a switch member operable between an open position and aclosed position for effecting the short circuiting of said resistor and the re-insertion thereof in the motor circuit, means responsiveto the moor current for controlling said switch member to effect the reinsertion of said resistor in the motor circuit, and electro-responsive means for holding said switch member in one of said positions to effect the short circuiting of said resistor while the motor current is less than a predetermined value and for holding the same in the other of said positions during the interval in which the motor current is temporarily reduced after the reinsertion of said resistor in the motor circuit.

4. The combination in a system of motor control of a resistor in the motor circuit, a contactor for short circuiting the said resistor, means responsive to the motor current for effecting operation of said contactor to reinsel't said resistor in the motor circuit, and a relay controlled by said means for controlling the said contactor to re-insert the said resistor in the motor circuit, the said relay having a switch member operable between an open position and a closed position and electroresponsive means for holding the said switch member in one of said positions to maintain the said resistor short cirouited while the motor current is less than the said predetermined value and for holding the switch member in the other of said positions during the interval in which the motor current is temporarily reduced after the re-insertion of said resistor.

5. The combination in a system of motor control of a motor, a resistor in the motor circuit, a switch member operable to the closed position to effect the short circuiting of saidresistor while the motor current is less than a predetermined value, means operated responsively to the motor current for eiiectinr operation of the said switch member to the open position to effect the re-insertion of said resistor in the motor circuit when the motor current is above the said predetermined value, an clectromagnet controlled by said means for operating the said switch member to the closed position and for holding the same in the closed positionwhile the motor current is less than the said predetermined value. and a second electromagnct controlled by said means for holding the said switch member in the open position while the motor current is te1npo l'ai'ily reduced after the ro-iuscrtion of said resistor in the motor circuit.

6. The combination in a system of motor control of a motor, a resistor in the motor circuit, a switch member movable between an open position and a closed position for controlling the said resistor, an electromagnet for holding the said switch member in the closed position and a second electromagnet for holding the same in the open position, means responsive to the motor current for controlling the said electromagnets to effect the short circuiting of said resistor when the motor current is less than a predetermined value and the re-insertion of said resistor in the motor circuit when the motor current. exceeds the said value, and means cooperating with said electromagnets for preventing the said first electromagnct from ettecting the short circuiting of said resistor during the inter al in which the motor current is temporarily reduced after the rcinsertion of said resistor in the motor circuit.

7. The combination in a system of motor control of a motor, a resistor in the motor circuit, a switch member movable between an open position and a closed position for .controlling the said resistor, an electromagnet for holding said switch member in the closed position and a second electromagnet having its winding connected in series relation with the winding of the first electromagnct for holding the said switch member in the open position, means responsive to the motor current for shunting the said first electromagnet to cause the said switch member to open and cifect the re'insertion of said resistor in the motor circuit when the motor current exceeds a predetermined value, and vmeans for preventing the said first elect romagnet from operating the said switch member to the closed position during the interval in which the shunt about the winding of the first electromagnet is temporarily opened in response to the temporary decrease of the motor current when the resistor is re-inserted in the motor circuit.

8. In a system of motor control, a resistor in the motor circuit, a controlling relay having a switch member for controlling the short circuitin of said resistor and the reinsertion thereo in the motor circuit, two electromagnets for controlling the said switch member, the first of said electromagnets being provided for holding the said switch member in the closed position to maintain the resistor short circuited and the second of said electromagnets being provided for holding the switch member in the open position to maintain the resistor re-inserted in the motor circuit, the windings of said relay being connected in series relation and arranged to be connected to a source of supply, a current limit slay for controlling the said controlling relay responsively to the motor current, connections whereby the said current limit relay shunts the winding of the first of said electromagnets to cause the said switch member to re-insert. the said resistor in the motor circuit when the motor currentexceeds a predetermined value and shunts the said second winding of said controlling relay to effect the short cireuiting of said resistor when the motor current is less than the said predetermined value, and a timing device. set. into operation by the shunting of said first winding for preventing the establishment of the shunt about said second winding during the interval in which the motor current is temporarily decreased after the re-insertion of said resistor in the motor circuit.

9. In combination, an alternating current motor of the slip ring type, a plurality of sections of resistance included in the secondary of said motor, a plurality of successive- 1y operated contactors for short circuiting the said sections, means responsive to the current taken by the motor for controlling the said contactors to shortcircuit the said sections successively during the acceleration of the motor, a relay governed responsively to the current taken by the motor for each of said contactors for effecting the prompt re-insertion of said sections of resistance m I the motor circuit in response to an overload on the motor of a predetermined value, the said relays constructed and arranged to prevent the subsequent short circuitingof said In witness whereof, I have hereunto set 

